The present invention is generally directed to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions comprised, for example, of toner resins, or polymers, pigment, and toner additives, such as charge control agents. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 0.5 to about 25, and preferably from 1 to about 10 microns and narrow GSD can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally a charge control agent or additive in water containing an ionic surfactant, and shearing this mixture with a latex mixture, comprised of suspended resin particles of from about 0.05 micron to about 1 microns in volume diameter, in water containing a counterionic surfactant in amounts of from about 0.5 to 5 percent (weight percent) of the mass of the latex with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant, thereby causing flocculation of the resin particles, pigment particles and optional charge control particles, followed by heating, below, for example from about 5.degree. to about 20.degree. C., the Tg of the resin, and stirring of the flocculent mixture which is believed to form statically bound aggregates of from about 0.5 micron to about 5 microns, comprised of resin, pigment and optionally charge control and thereafter heating at, for example, from about 10.degree. to about 50.degree. C., above the Tg of the latex resin to generate toners ,with an average particle volume diameter of from about 1 to about 25 microns and wherein the concentration of the latex is decreased from 40 percent to 1 percent by weight of the total suspension of latex, pigment, surfactant in water and preferably from 30 percent to 5 percent by weight in the aggregating suspension while maintaining the same or similar coagulant surfactant/latex surfactant ratio of from about 0.5:1.0 to 4:1 thereby enabling the formation of toner aggregates the size of which depend primarily inversely on the latex particle concentration in the blend. Specifically for example, the size of the aggregate produced when a particular latex is aggregated in this manner, under conditions where the ratio of counterionic surfactant coagulant to latex ionic surfactant is fixed, is small, for example 2 microns in volume average diameter at high latex loadings (30 percent solids) and larger, for example 8 microns in volume average diameter at low loadings (5 percent solids). The process of aggregating identical lattices at differing solids loadings of the latex in the dispersion while maintaining a constant ratio of counterionic surfactant coagulant to latex ionic surfactant ensures aggregates of a uniform chemical composition and allows for the formation of a wide variety of toner particles of preselected sizes, each with a narrow size distribution (GSD) of, for example, from about 1.16 to about 1.26 as measured on the Coulter Counter. It is believed that during the higher temperature heating stage, the aggregate particles fuse together to form toners. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in water containing a cationic surfactant such as benzalkonium bromide (SANIZOL B-50.TM.), utilizing a high shearing device such as a Brinkmann Polytron, microfluidizer or sonicator, thereafter shearing this mixture with a latex of suspended resin particles such as PLIOTONE.TM., comprised of poly(styrenebutadiene) and of particle size ranging from 0.01 to about 0.5 micron in average volume diameter as measured by the Brookhaven nanosizer, in an aqueous surfactant mixture containing an anionic surfactant such as sodium dodecylbenzene sulfonate (for example NEOGEN R.TM. or NEOGEN SC.TM.) and nonionic surfactant such as alkyl phenoxy poly(ethylenoxy)ethanol (for example IGEPAL 897.TM. or ANTAROX 897.TM.), thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which on further, from for example about 1 to about 3 hours, stirring while heating below the Tg of the latex resin results in formation of statically bound aggregates ranging in size of from about 0.5 microns to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II); and thereafter heating to, for example, from about 5.degree. to about 50.degree. C. above the Tg of the latex resin, of, for example, from about 60.degree. to about 95.degree. C., to provide for particle fusion or coalescence of the polymer and pigment particles; followed by washing with, for example, hot water to remove surfactant, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to 12 microns in average volume particle diameter and wherein the solids loading of the latex in the dispersion is decreased by diluting with water from the range of about 40 percent to 2 percent with a preferred range of decrease being from about 30 percent to 5 percent. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present.
While not being desired to be limited by theory it is believed that the flocculation or heterocoagulation is formed by the neutralization of the pigment mixture containing the pigment and cationic surfactant absorbed on the pigment surface, with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. The high shearing stage ensures the formation of a uniform homogeneous flocculated system, or gel, from the initial inhomogeneous dispersion which results from the flocculation action, and allows the formation of stabilized aggregates that are negatively charged and comprised of the resin and pigment particles of about 0.5 to about 5 microns in volume diameter. Thereafter, heating is applied to fuse the aggregated particles or coalesce the particles to toner comprised of polymer and pigment, and optionally charge control agent. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by homogenization, to form statically bounded aggregate particles by stirring of the homogeneous mixture, and toner formation after heating. The latex resin particles for the aggregation is selected for its functional performance in the xerographic process, especially the process involved with fixing the image to the final receptor medium, usually paper. The utilization of a constant counterionic pigment dispersion surfactant to latex surfactant ratio when aggregating the latex under differing solid loadings ensures a consistent toner chemical composition while also providing a means to obtain narrow size toner distributions. The solids content decrease by diluting with water enables, for example, toner particle size control.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns have been effectively utilized. Moreover, in some xerographic systems, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with an average volume particle of less than 11 microns, preferably less than about 7 microns and more preferably from 1 to about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.2 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized such as pictorial color applications, small particle size colored toners of from about 3 to about 9 microns are desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes such as from about 1 to 7 microns and with higher pigment loading such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures such as from about 120.degree. to about 150.degree. C. thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, when a low gloss image of preferably from about 1 to about 30 gloss is preferred, low gloss paper is utilized such of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners of from about 3 to about 5 microns and fixing thereafter results in a low gloss toner image of from above about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, when higher image gloss is desired, such as from about above 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized such as from above about 30 to about 60 gloss units, and which after image formation with small particle size toners of the present invention of from about 3 to about 5 microns and fixing thereafter results in a higher gloss toner image of from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns such that the pile height of the toner layer(s) is low.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 9 microns to about 20 microns and with broad geometric size distribution of from about above 1.4 to about 2.0. In such processes it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 5 microns are attained without resorting to classification processes, and where in narrow geometric size distributions are attained, such as from about 1.16 to about 1.35, and preferably from about 1.16 to about 1.30. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of the present invention in embodiments, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer such as acrylic acid in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention need not utilize polymers with polar acid groups, and toners can be prepared with resins such as poly(styrenebutadiene) or PLIOTONE.TM. without containing polar acid groups. Additionally, the toner of the '127 patent does not appear to utilize counterionic surfactant and flocculation processes. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. Furthermore, the '488 patent does not, it is believed, disclose the process of counterionic flocculation, and the importance of solid contents to control particle size. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of oppositely charges are selected; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other patents mentioned are 3,674,736; 4,137,188 and 5,066,560.
In U.S. Pat. No. 5,290,645, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent, and a polyester and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising an halogenization procedure which, for example, chlorinates the outer surface of the toner and results in enhanced blocking properties. More specifically, this patent application discloses an aggregation process wherein a pigment mixture, containing an ionic surfactant, is added to a resin mixture, containing polymer resin particles of less than 1 micron, nonionic and counterionic surfactant, thereby causing a flocculation to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites or toner compositions of from about 3 to about 7 microns in volume diameter.
In U.S. Pat. No. 5,308,734, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant, adding thereto a counterionic surfactant with a polarity opposite to that of said ionic surfactant, homogenizing and stirring said mixture, and heating to provide for coalescence of said toner fine particles.
In copending patent application U.S. Ser. No. 022,575 (D/92577), the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in a water, which dispersion is comprised of a pigment, an ionic surfactant and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form electrostatically bound toner size aggregates; and PA1 (iii) heating the statically bound aggregated particles to form said toner composition comprised of polymeric resin, pigment and optionally a charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, an ionic surfactant and an optional charge control agent; PA1 (ii) shearing at high speeds the pigment dispersion with a polymeric latex comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, and a nonionic surfactant thereby forming a uniform homogeneous blend dispersion comprised of resin, pigment, and optional charge agent; PA1 (iii) heating the above sheared homogeneous blend below about the glass transition temperature (Tg) of the resin while continuously stirring to form electrostatically bound toner size aggregates with a narrow particle size distribution; PA1 (iv) heating the statically bound aggregated particles above about the Tg of the resin particles to provide coalesced toner comprised of resin, pigment and optional charge control agent, and subsequently optionally accomplishing (v) and (vi); PA1 (v) separating said toner; and PA1 (vi) drying said toner. PA1 (i) preparing by emulsion polymerization a charged polymeric latex of submicron particle size; PA1 (ii) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an effective amount of cationic flocculant surfactant, and optionally a charge control agent; PA1 (iii) shearing the pigment dispersion (ii) with a polymeric latex (i) comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form a high viscosity gel in which solid particles are uniformly dispersed; PA1 (iv) stirring the above gel comprised of latex particles, and oppositely charged pigment particles for an effective period of time to form electrostatically bound relatively stable toner size aggregates with narrow particle size distribution; and PA1 (v) heating the electrostatically bound aggregated particles at a temperature above the resin glass transition temperature (Tg) thereby providing said toner composition comprised of resin, pigment and optionally a charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent; PA1 (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution; PA1 (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); and PA1 (v) heating and coalescing from about 5.degree. to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. to about 90.degree. C. and preferably from between about 50.degree. and about 80.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, ionic surfactant, and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a polymeric latex comprised of resin of submicron size, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent, and generating a uniform blend dispersion of solids of resin, pigment, and optional charge control agent in the water and surfactants; PA1 (iii) (a) continuously stirring and heating the above sheared blend to form electrostatically bound toner size aggregates; or PA1 (iii) (b) further shearing the above blend to form electrostatically bound well packed aggregates; or PA1 (iii) (c) continuously shearing the above blend, while heating to form aggregated flake-like particles; PA1 (iv) heating the above formed aggregated particles about above the Tg of the resin to provide coalesced particles of toner; and optionally PA1 (v) separating said toner particles from water and surfactants; and PA1 (vi) drying said toner particles. PA1 (i) preparing a pigment dispersion, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent; PA1 (ii) shearing said pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant; PA1 (iii) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; and PA1 (iv) heating said bound aggregates above about the Tg of the resin.
Disadvantages that can be associated with the process of U.S. Ser. No. 022,575 (D/92577) is that toners of different size cannot usually be obtained, rather the size of the toner is altered only by alteration of the starting latex resin size and composition and the quantity of coagulant added to form the aggregates. When toner particles are prepared by varying the coagulant/resin ratio the chemical composition of the obtained toner, particularly the surface properties of the toner, can differ from one aggregate size to another, and this can cause differences in the xerographic behavior of the material as indicated in U.S. Pat. No. 5,213,938, the disclosure of which is totally incorporated herein by reference, since, for example, the xerographic toner charging process is, for example, very dependent on the toner surface chemistry.
In copending patent application U.S. Ser. No. 082,651, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
In copending patent application U.S. Ser. No. 083,146, (not yet assigned D/93106), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with a volume median particle size of from about 1 to about 25 microns, which process comprises:
In copending patent application U.S. Ser. No. 083,157, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
In copending patent application U.S. Ser. No. 082,741, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size and selected morphology comprising
In copending patent application U.S. Ser. No. 082,660, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising: